摘要:
提要: 本文主要对出露与西藏多龙矿集区铁格隆南矿区荣那矿段的安山岩开展了锆石U?Pb定年、岩石地球化学测试, 旨在确定该套火山岩的成岩年龄及其形成的构造背景。安山岩的LA?ICP?MS锆石U?Pb加权平均年龄为(110.1±0.7) Ma (MSWD=2.3), 代表了其成岩年龄。岩石SiO2为59.5%~61.48%; Al2O3为16.14%~17.11%; Na2O+K2O为6.02%~6.63%; Mg#值中等, 微量元素富集Ba、Rb、Th、K等大离子亲石元素, 相对亏损Ta、Nb、P、Ti等高场强元素, 具有Rb正异常和明显的Zr、Hf负异常, 据此认为该安山岩属高钾钙碱性系列岩石, 具有活动大陆边缘火山岩的性质, 是班公湖—怒江洋北向俯冲, 拉萨地体与羌塘地体碰撞拼贴过程中所诱发的岩浆产物。结合其他资料分析认为, 此安山岩的成岩时间应晚于铁格隆南高硫型浅成低温热液铜(金)矿床的成岩和成矿时间, 是该矿床得以良好保存的重要条件。
Abstract:
Abstract: In this paper, the authors studied the andsites in Rongna ore block, Tiegelong Cu (Au-Ag) deposit, Duolong ore concentration area, Tibet, and used the zircon U-Pb data and petrogeochemistry of andsites to identify the petrogenetic age and tectonic setting of the andsites. The weighted average age of zircon U-Pb is 110.1±0.7 Ma (MSWD=2.3) , which represents the petrogenesis age. An analysis of the whole rock sample shows that SiO2 values are 59.5%-61.48%, Al2O3 values are 16.14%-17.11% and Na2O+K2O values are 6.02%-6.63%; Mg# is of intermediate value. LILE such as Ba, Rb, Th, K are rich, HFSE such as Ta, Nb, P, Ti are relatively poor and characterized by Rb positive anomaly and obvious Zr, Hf negative anomalies. Petrological and geochemical studies show that the andesites are high potassium calc-alkaline rocks exhibiting the characteristics of Andean-type active continental margin volcanic rocks. They resulted probably from partial melting of subducted oceanic slab as well as miscibility with crustal material during the upward migration of the magma in the case that subducted oceanic slab didn’t interact with the mantle. They were the magma products of the northward subduction of Bangong Co-Nujiang Ocean and Lhasa and the collision collage process of Qiangtang terrane. In combination with other dating data and drilling core catalog data, the authors hold that the formation of andesites was later than the rock-forming and ore-forming stage of the Tiegelongnan high sulfur epithermal Cu (Au-Ag) deposits, which seems to have been the important condition for the preservation of the ore deposit.
百度学术
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